<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<script>
			function output(y,m,d){
				alert(y+"年"+m+"月有"+d+"天");
			}
			function days(y,m){
				if(m == 2){
					if((y%4 == 0 && y%100 != 0) || (y%400 == 0)){
						output(y,m,29);
					}else{
						output(y,m,28);
					}
				}else if(m == 4 || m == 6 || m == 9 || m == 11){
					output(y,m,30);
				}else{
					output(y,m,31);
				}
			}
			days(2021,6);
		</script>
	</body>
</html>
